Cause : DC Bus Undervoltage comes when the DC bus voltage is ≤ L2-05 208-240Vac: Trip point is ≤ 190Vdc 480Vac: Trip point is ≤ 380Vdc. 

When one of the following conditions was true when the drive was stopped and a Run command was entered:
• DC bus voltage dropped below the level.
• Contactor to suppress inrush current in the drive was opened.
• Low voltage in the control drive input power.

1. Phase loss in the drive input power.
2. Check for wiring errors in the main circuit drive input power. Correct the wiring.
3. Loose wiring in the drive input power terminals.
   • Ensure the terminals have been properly tightened.
   • Apply the tightening torque to the terminals as specified.
4. There is a problem with the drive input power voltage.
   • Check the voltage.
   • Lower the voltage of the drive input power so that it is within the limits listed in the specifications.
5. Drive internal circuitry is worn.
   • Replace either the control board.
6. The drive input power transformer is too small and voltage drops when the power is switched on.
   • Check for an alarm when the magnetic contactor, line breaker, and leakage breaker are closed.
   • Check the capacity of the drive input power transformer.
7. Air inside the drive is too hot. Check the temperature inside the drive.